This invention relates to a coating for use on polymeric substrates, and more particularly, to a coating which provides low temperature heat sealability and high hot tack to such polymeric substrates.
In the packaging industry, heat-sealable films are often employed which can be sealed to themselves. For example, polymeric films such as biaxially oriented polypropylene are often used in packaging candy bars and other foods by the application of heat and pressure, which seals the film to itself or to another substrate. However, as such films generally exhibit poor heat sealing characteristics, a coating is typically applied to the film which allows the film to be sealed over a relatively wide temperature range and which adheres securely to the film surface. Heat sealable coatings are known in the art which are comprised of copolymers of ethylene and acrylic acid, vinyl acetate, or vinyl alcohol. See, for example, U.S. Pat. Nos. 5,419,960 and 6,447,899.
However, heat seal coatings which are currently in use typically require sealing temperatures of at least about 90° C. Further, such coatings often do not provide satisfactory hot tack properties to the film, i.e., the strength of the heat seal provided when the coating is heated to a temperature at or above the melting point of the polymer coating.
In addition, many of the coatings currently do not adhere well to the packaging film surface and require the use of a primer to aid in enhancing adhesion of the heat sealable coating to the film surface.
Accordingly, there is still a need in the art for a coating for use on polymeric substrates which provides low temperature heat sealability as well as high hot tack, and which adheres well to the substrate surface without the need for the application of additional precoatings and primers.